caffeine

noun

caf·​feine ka-ˈfēn 

ˈka-ˌfēn

: a bitter alkaloid C₈H₁₀N₄O₂ found especially in coffee, tea, cacao, and kola nuts and used medicinally as a stimulant and diuretic

Examples of caffeine in a Sentence

Her doctor told her to avoid caffeine.

Recent Examples on the Web

Stress, caffeine, medications, alcohol, and illness can all increase your heart rate, while relaxation techniques can lower it. — Zoe Cunniffe, HEALTH, 5 Aug. 2026

The average caffeine consumption is 3 cups per day,2 but how good can drinking this much coffee so early in the day be? — Erin Hooker Published, Better Homes & Gardens, 4 Aug. 2026

Most herbal tisanes are naturally caffeine-free, but those with yerba maté, guayusa, or cacao have some caffeine. — Christopher Bergland, Verywell Health, 3 Aug. 2026

The first looks at your sleep patterns over time, while sleep stress can be an indicator of when exercise, alcohol and caffeine too late in the day are affecting your sleep. — Andrew Williams, Forbes.com, 31 July 2026

Word History

Etymology

German Kaffein, from Kaffee coffee, from French café

First Known Use

circa 1823, in the meaning defined above

Phrases Containing caffeine

• caffeine-free

Rhymes for caffeine

• agin
• alkene
• allene
• ameen
• amin
• arene
• athene
• baleen
• beeline
• benzene
• between
• bromine

Kids Definition

caffeine

noun

caf·​feine ka-ˈfēn 

ˈka-ˌfēn

: a bitter stimulating compound found especially in coffee, tea, cacao, and kola nuts

Medical Definition

caffeine

noun

caf·​feine ka-ˈfēn, ˈka-ˌ; ˈkaf-ē-ən 

: a bitter alkaloid C₈H₁₀N₄O₂ found especially in coffee, tea, and kola nuts and used medicinally as a stimulant and diuretic

caffeinic

ka-ˈfē-nik  ˌkaf-ē-ˈin-ik 

adjective